Stable element gyro



Aug. 22, 1950 c. R. HANNA ETAL STABLE ELEMENT GYRO 2 Sheets-Sheet 1 Original Filed March 1, 1944 INVENTOR5= C1./- TON R. HANA/H. LAWRENCE 5. LY/V/V.

lll l WITNESSES:

ATTORNEY g- 22, 1950 I c. R. HANNA El'AL 2,519,459

I STABLE ELEMENT GYRO Original Filed March 1, 1944 2 Sheets-Sheet 2 WITNESSES: INVENTORS: 6 CL/NTo/vR? HANNA. LAWPENCEB. LYNM 9% 03- BY a. as 68AM;

ATTORNEY i 'atented Aug. 22, 1950 STABLE ELEMENT GYRO Clinton R. Hanna, Pittsburgh, and Lawrence B.

Lynn, Wilkinsbung, Pa.,. assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania .Original application March 1, 1944, Serial No. 524,560. Divided and this application August 27, 1946, Serial No. 693,208

Claims.

Serial No. 524,560, filed March 1, 1944, Patent No. 2,457,228, granted December 28, 1948, for Stable Element and is concerned with the gyro and related features.

with a neutral gyro having its rotor spin axis constrained to the vertical, means acting in a north-south plane to cause the gym to precess in the east-west plane at the same rotational ve- This application is a division of our application A further object of the invention is to provide} locity as that of the earth and in the same direction as the latter so that the rotor spin axis may be maintained vertical.

Another object of the invention is to provide a neutral gyro having an improved magnetic erector together with means for compensating for the effect of earths rotation.

A more particular object of the invention is to provide, with a neutral gyro, means responsive to gravity and acting on the gyro to cause the spin axis to seek a directional position in relation to the earth, together with means for applying torque to the gyro about an axis transverse to the spin axis and for maintaining the torque in a north-south plane to correct for the effect of earths rotation on the gyro.

A further object of the invention is to provide a gyro-vertical wherein the gyro is acted upon by means responsive to gravity so that the spin axis seeks the vertical and the gyro is acted upon by magnetic means applying torque thereto in a north-south plane to correct for the effect of earth's rotation thereon.

A further object of the invention is to provide eddy current damping means for the pendulous suspension of-the magnetic erector.

A further object of the invention is to provide a gyro having its spin axis constrained to vertical position together with a friction damper effective horizontally and rotationally to damp mutational oscillations.

These and other objects are effected by the invention as will be apparent from the following description and claims taken inconnection with the accompanying drawings, forming a part of this application, in which:

Fig. 1 is a view, partly in section and partly in elevation, showing the improved gyro-vertical;

Fig. 2 is a sectional view taken along the line IIII of Fig. 1; 7

Figs. 3 and 4 are detail views showing a modified form of the pick-up means operated by the y r Fig. 5 is a diagram showing geometric rela- 5 tions of the structure shown;

An object of the present invention is to pro- Fig. 6 is a vertical diametrical sectional, View of the nutational damper.

In the drawings, there is shown a neutral gyro comprising a housing or frame in having a motoroperated rotor l| journaled therein and supported by gimbal means from a suitable supporting structure. Thegimbal means includes a gimbal ring l2, inner pivots l t-l4 for supporting the housing or frame from the gimbal ring, and outer pivots I5l5 for supporting the gimbal ring from suitable supporting tructure. Designating the rotor spin axis as y1y1, the axis of the inner pivots M-M as rel-x1, and the axis of the outer pivots I 5-l5 as z1z1, it will be noted that the inner gimbal axis :m-x1 is at right angles both to the outer gimbal axis 21-21 and the rotor spin axis y1-y1 and that all three of such gyro axes have a common point of intersection 0.

As more fully disclosed in the application aforesaid, the supporting structure comprises a rotatable yoke IS, a cross level ring i9, and a level 20, the level being supported from the cross level by pivots 2l2l and the cross level being supported from the yoke by pivots 22-22, Designating the yoke axis as -g, the cross level axis as :c :r and the level axis as zz, such axes have a common point of intersection and the gyro is supported with respect to the supporting structure so that its center ll is coincident with such point of intersection. The relationship of gyro axes and supporting structure axes such that all of such axes intersect at a common point 0 is indicated by Fig. ,5, from which it will also be seen that the cross level and level axes, the gyro gimbal axes, and the erector gimbal axes are in normal planes intersecting at the yoke axis.

7 With means acting on the gyro to keep the spin axis vertical and with suitable follow-up means controlled by the gyro and capable of moving the cross level and the level about thecross level and level axes, it will be apparent that, irrespective of deviation of the yoke axis from the vertical and occasioned, for example, by rolling and pitching of the ship upon which the yoke is mounted, the cross level is moved about the cross level axis to keep the level axis horizontal and the level is moved about the level axis to maintain a predetermined plane thereof level or horizontal. As shown, the yoke carries a cross level motor 3 4 25 operative to move the cross level about the the gyro ente a, self-oscillation of t magcross level axis and the cross level carries a level net tends to occur because it is free to react to motor 26 operative to move the level about the the electro-magnetic drag which it exerts n the ve a e S pp Structure, pfeferab1y gyro f ywheel structure; and, to minimize oscilthe level 20, carries pick-up devices 21-21 for :lations ori=that.account,lthere:is provided an eddy the cross level servo-motor system and pick-up rr nt amper-e3 effective o the pendulous devices 28-28 for the level servo-motor system. A mounting about the axis of one of the sets of In Figs. 1 and 2, the pick-up devices are variable pivots, for example, the pivots 35 35,

resistances in direct current circuits of the cross 'Where'.the gyro and the erector are carried level and level follow-up motors and such de- 0 by a cage mounted on the level, the intersection vices are operated by the-actuator-29 carried by of thegyro=axesstill coinciding with the interthe gyro casing In in axiaralig m nt' with' t sectiono'f the-cross level and level axes, and the spin axis. cage is slowly"rotated to avoid mechanical and Any tendency of the level to deviate from its thermal errors, as disclosed and claimed in the vertical or horizontal positionbecauseof move-1 5 applicatiorrcf Lynn;1SerialNo. 607,711, filed July ment about the cross level-axis,andrinstheplane '30,:1945,I PatentsNo. 2,417, 081, granted March of the level axis, results in actuation of the pick- 11,- l97g and where the bail of the erector magup devices 21-47 and consequent operation of net pendulous suspension is pivoted directly on the cross level motor 25 to move thecross' level the gyro ginibal pivots l5l5, instead of through to maintain the level axis horizontal and any a gimbal ring, the magnet has freedom of motion tendency'of the level to deviate because-of move- "and" response to 'gra'vity'o'nly-in a plane perment'about'the level axis'andinthepl'ane ofthe -pendicular toits suspension axis-and it cannot cross level axis results in operation of the pick-up react to the electromagneticdrag and thus pick devices-28-28 and consequent-*operationof the up energy for-self' oscillation from the flywheel. level motor 26 to move the-level about the-level Therefore, the necessity for damping is'avoided axis. and it becomes-feasibletoiuse-a larger erecting Therefore, where theyoke is moved angular-1y current with a consequent larger erecting torque. '--'a.bout the cross level and-level axes; aswould be 5 Inall'cases 'the' gyro center coincides with the the case where it is earriedby-the'deck of 'a ship, point of --intersection'of the principalaxes of the then, irrespective of rolling and pitching, the stable element, that is, the cross level and level gyro-vertical controls the cross level and level axes are in planes -whichintersectat right angles "servo-motor systems to move the cross'level'and atthe train'or yoke; axisand the coincident gyro level about their axes sufficiently-to maintain the center and'intersection'of the cross-level and level 'level vertical or with a predetermined plane axes is on such trainor-yoke ax-is;- the cross level thereof horizontal. I and level servo-motor means pick-up-devices are Togive the neutral gyro-a vertical-seeking arranged-for' actuation' by -movements in level tendency, there is provided-a magnetic erector, and crosslevel planes; respectivelyy'the spherical 'at 30. The erector comprises a 1 magnet --3l surface of the erector is centeredwith respect to pendulously sup-ported so that its axis 'is'in the the gyro center;- and the 1 erecting magnet is -'ver-tical passing through the gyro center *0. pendulouslysuspendedwith-respect to the gyro The pendulous mounting is provided by a 'bail center orat lea'st'with respect to the outer gimbal H -supported by pivots" 33-33-'from the gimbal axis of the gyro. "ring 34, which is pivoted at 35- 35'with respect In--ad=dition to theaforesaid-means acting on to the gyro gimbal outer pivots l5-I5. "the neutral-gyro- -in response to gravity to give I The gyro rotor -has'a circular coaxial'met'allic to the spin axis the tendencyto seek a directional "portion 36 rotatable therewith and 'having -a positiorr in relation to the earth, "more particul-spherical surface 31 whose center is the gyro 3, to e thewer'tical, there is p center and the surface beingwspaced to'define' a m n for pp yin q e he yro abo n .suitably au air gapwithrespe'ct t -the-magnet :axisfitransverse to the spinaxisand in a north- With this arrangement, rotation ofthe' flywheelpo p e o rr c or h ff c of earths portion 36 in the field of-themagnet-induces rotation on the'lgyro.itheltolquewlpplying mea s "eddy currents therein responsible for" magnetic bein fl i b o'suitthe latitude. "drag exerted on the rotor. As long as-the spin The torque about an axis transverse to the spin a'xis isvertical, the drag merelyappliesa' torque axis is prefe y pp y magnetic eans about the spin axis opposed to the-direction' of; mpr -w e mp en nd an armaspin; however; deviation of -the-spin axis-from t11rB 0r magnet c0mponent,-oneof the c0ml the vertical results in awcou'ple apialiedtothe nents being'cylindricalfllid' attached to the y o gyro t precess t e tt in o osition-t 'th frame [0 and the other component-being movable v deviation. "For example, assuming deviation ou the cylindrical component vary the p irom the vertical iby movement 'about the gyro; tion of the torque plan-e. -For examp1e, there is axis xr-an, then such deviation results 'in the shown a cylindric'ahcomponent-'40 carried by the magnetic erector applying a couple aboutthe 'gyro'frame lll'ln axial-"alignment with the spin gyro-axis 2121 which causes precession about 'axis'and providing witha winding ll,the core t g opposing the deviation. In like structureandwinding"constituting a'cylindrical 'manner, deviation from the vertical abouttheaxis 'electromagn'et. The armature*orrmagnetibar' 42 'zi- -zi is accompanied-by torqueapplied aboutthe is supported from the level 20*by'a-motor 43 'axis :c1a:1 to effect precessionin opposition to which is operated to'move the'armature' or bar \thedeviation. :Therefore, deviation of the spin about themagnet-tom'aintain the plane of the axis about. either or both of the gyrogimbal axes applied torque "in the north-south plane. u-esults in the application'of couple or couples to :7 Themagnetic-torque is varied to suit the lati- :precess the gyro to the'vertical; that is; not only tude, this purpose being 'achievedfforexample, iisdeviation from the vertical opposedrbut the by the variable resistance fl inthe'winding cir- :spin axis is restored to thelver-tical. cuit- 45. "-Wherethespin axis directional'posi- :As the magnet of the erector ispendulously tionis' the vertical, it vvill be'apparent that the 'supported inai universalanannerewith respect tic-7175 tendency of the earth's rotation is todeviate the as the equator is approached. Furthermore, the

resistance may be located remotely in relation to the gyro with obvious operating advantages over the old arrangement of an adjustable weight carried directly by the gyro to compensate for earth's rotation.

In order that the motor 43 may function to keep the armature in a north-south plane, it is of the synchronous type and is connected to a suitable generator 46 operated by the compass, at 46a. As shown, the synchro-motor 43 and the synchro-generator 46 have single-phase windings 41 and 43 and three-phase windings 49 and 50, respectively. The single-phase windings are excited from a suitable source of single-phase alternating current and the three-phase windings are joined by the three-phase line 52. The synchronous connection serves to keep the armature matched with the compass to maintain the armature in a meridian plane. With a change in course of the ship, the armature would be correspondingly changed but for the synchronous connection to the compass, the synchro-generator voltage energizing the synchro-motor to keep the armature matched with the compass, that is, in the north-south plane.

The synchro-motor 43 is preferably mounted on the level 26 by means of supporting or bracket structure 54, the motor being mounted so that its rotor 55 is axially aligned with the spin axis with the level horizontal and the spin axis vertical. The rotor 55 has a non-magnetic crank arm 56 carrying the armature or magnet bar.

While it is immaterial What kind of electrical follow-up system is operated by the gyro to control the cross level and level motors, in Figs. 1 and 2, the pick-up devices 27-21 and 2328 control the supply of direct current to the motors 25 and 26, respectively, for operation of the latter in either direction, dependent upon departure from the vertical; and, in Figs. 3 and 4, there are shown magnetic pick-up devices 2'la2'la and 28a28a for cross level and level follow-up systems of the alternating current type, such pick-up devices having their magnetic reluctances varied by means of the armature element 29a which cooperates with air gaps thereof.

The frame or casing in for the rotor is provided with a damper, at 65, to dissipate nutational vibration energy. The damper includes a casing 6| carried by the rotor frame or casing above the rotor and providing an -annular chamber 62 coaxial with the spin axis and within which is located an annular inertia member or mass 63, preferably having an outer annular rib i; l

54 at its lower side and adapted to bear on the normally horizontal bottom surface of the chamber. The inertia member or mass 63 has clearance with respect to the inner and outer peripheral walls 65 and 66 of the chamber as well as with respect to the top and the bottom wall except for the rib bearing area on the latter. It will be apparent that the inertia of the mass 63 is effective horizontally and rotationally, any movement of the casing being opposed by the inertia of the mass to the extent of the frictional resistance between the mass and the chamber bottom. Hence, the apparatus functions as a damper to dissipate or absorb vibration energy by friction with the result that nutational eifects are minimized. The damper is useful to absorb nutational vibrations where the gyro has its spin axis constrained to its vertical position, this being particularly true in the apparatus illustrated and described and in which the erector takes the form of a pendulous member which acts across clearance with respect to the lower portion of the rotor to cause the latter to act gyroscopically to return the spin axis to vertical in the event of departure thereof therefrom.

While the invention has been shown in several forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof.

What is claimed is:

1. In a neutral gyro, a rotor assembly comprising a frame or casing carrying a rotor, a pendulous erector cooperating with the rotor to bring the spin axis to vertical position, a damper for damping pendulous movements of the erector and operative independently of the gyro, and a damper for minimizing nutational movements of the gyro, said nutational damper comprising means carried by the frame or casing above the rotor and providing an annular chamber coaxial with the rotor spin axis and having a horizontal interior bottom surface and an annular inertia member within the chamber, bearing on said bottom surface, and having clearance with respect to the inner, outer and. top walls of the chamber so as to be capable of movement relative to the casing in response to nutational vibratory motion to frictionally dissipate the nutational vibratory energy.

2. In gyro apparatus, a support movable angularly with respect to the earth; an operated member; a neutral gyro; gimbal means for supporting the gyro and the operated member from the support; gravity-responsive means carried by the gimbal means and acting on the gyro so that the spin axis has a directive effect in relation tothe earth; follow-up means responsive to the gyro to move the operated member relative to the support to maintain its position irrespective of angular movement of the later; electromagnetic means operative independently of said gravity-responsive means for exerting torque on the gyro in a north-south plane and about an axis transverse to the spin axis to minimize deviation of the latter from its directing position: said electromagnetic means including a pair of permeable magnetic flux path components, which are carried, respectively, by the operated member and by the gyro and are separated by an air gap, and a flux-producing winding carried by one of said components; and means for varying the exciting current of said winding so as to correct substantially for variation in latitude.

3. In gyro apparatus, a support movable angularly with respect to the earth; a neutral gyro; an operated member; gimbal means for supporting the gyro and the operated member from the support; gravity-responsive means carried by said gimbal means and acting on the gyro to cause the spin axis to seek a directing position in relation to the earth; follow-up means responsive to the gyro to move the operated member relative to the support to maintain its position irrespective of angular movement of the latter; electromagnetic means for exerting torque on the gyro about an axis transverse to the spin axis; said electromagnetic means including a pair of winding and armature components of which one is cylindrical and the other is arranged for movement- :1 thereabout' in. spaced l re1aifiorr.. thereto;: means. for mounting the-- cylindrical "component: onxthegyro in coaxialrelationwith thel rotor spinaxis means. including a motor 1 or: mounting the other component on. the 'operat'edlmembenand' the motor beingoperative tO ZmO V-B':ZSZI. l'd.- other component about. the cylindrica1= component. to. locate. thetorque inia no1'th.-south..-plane.;:and means .for varying. theexciting .current 'ois the winding to correct. for variation in. latitude-t.

4.. In gyro apparatus, asupport'movableangularly with respectto the earth; an operated memv-l her; a. neutral gyroi; gimbal. means forxsuppoirt-u ing the gyro and operated 'memberiromcthesupport; gravity-responsive" means: carried by the. gimbal means and acting on .thegyroinzresponse to departure ofthe spin axis from. the-vertical to cause it to process to oppose such. departure and to restore the spin axis. to vertical; means for exerting torque onthe gyro in-a north-south 4 plane to cause it to precessin the east-west plane. to compensate for the efiect of earthfs. rotation. to maintain the spin axis vertical; said lastnamed means including a pair. of spaced compo-.

nents carried by the gyro and by the operated.

member and which cooperate. to provide a.mag-' netic flux circuit such that thefiux exerts attractive force to provide said torque; andmeans. providing for magnetic flux in. said circuit.

5. Apparatus as claimed in claim4 with means providing for variation of the. flux oi said.circuit. to vary the attractive force to suit the latitude so that the gyro may be. caused toprecess inan east-west plane at the same rotational velocity as that of the earth and in the same direction as that of the. latter.

6. In gyro apparatus, a support movable angu-l larly relative to the earth; .a level member; a neutral gyro comprising a frame and :a-1.rotor:

journaled in the frame; .gimbal" means for sup.-

porting the level member and the gyro from-the support; gravity-responsive meanscarried by. the gimbal' meansand acting on the gyro in response. todeparture of the rotor spin axis from vertical. toapply torque thereto to causethe: gyro .tct precess to-oppose-such departureland to: restore the spin axis to vertical; follow-uptmeansz re-z sponsivetothe gyro to move the level memberv relative'to the support to maintain its position. irrespective of angularmovement of the latter; electromagnetic: means for eXertingJattractive force onthe gyroin a north-south plane; to: cause it to precessi'nthe east-westplaneto.maintain the spin axis vertical;v saidelectromagnetic.

means comprising a winding component. and .an; armature component 'cooperatingctherewith;.to:

develop 1 the attractive magnetic: force. .androne of. saidcomponents. being cylindrical; means for. mounting the cylindrical component on the gyro frame in coaxialrelation with the rotor. spinaxis; means including a motor. for mounting theother component on the level memberxand. the motor. being operative to move such other component about the cylindrical component. 3 so that. :the

attractive 'magnetic force may be exerted 0111 thegyro in the north-south plane; andmeanspro viding exciting current for thewinding. of the: Winding component.

7. In gyro apparatus, a support movable angus larly with respect to the earth; a levelmember; a neutral gyro including a casing and' a rotor journaledtherein; a pendulous member; 'gimbal: means for supporting the level and pendulous members and the gyro from the support; means carried by the pendulous member and. acting on the: gyro tocausexlthe rotor. spim axis storprecess to thevertical; the last-named'means: comprise ingan electromagnet carried by. the pendulous member and: acircular. metallic member. forming a coaxial apart. or. the gyro rotor androtated con-1 tiguously to: the electromagnet to produce,. de-.. pendent. upon the deviationoi the rotor'spimaxis: from vertical and dueto eddyrcurrent actionyo couple/acting 'Onithe. gyro to.- precessthe spin axis to.= =vertical; whereby deviationof. the spiruaxis from vertical is opposed and such.spin; axissis returnedlto' vertical-5 electromagnetic meansJor exerting torque on the gyro in. .a.-.northesouth1 plane .to' cause. the gyro-to precess. in. the east-t westz'plane; said electromagnetic meansinclud-e ing a ;pair. of winding and. armature components of whichone is cylindrical and the other; is .ar: ranged for. movement thereabout: in .spaced arela' tion thereto;. means for. mounting. thecylindrical' eoniponent; on. the gym and; in.- coaxial. relation; withthe rotor spinaxis; meanslincludingramotor. for mounting the other. component. onitherlevel: member and the: motor: being: operative .to a move such other: component: about. the-cylihdricall com penentnto .locate the. torque. inv -a. north-south: plane; andi means. forv .varying .the exciting cur-- rent: ofiithev/inding. component to. correctionvariationzin'latitudea.

8. Ingyro apparatus,..a support: movable .angu-. larly .\vith respect.to the earth; alevel member; a neutral gyro comprising airameoncasingand aro-torjournaled inathe latter; a pendulous member; gimbalmea-ns'for supporting the .1evel...and.- pendulouss. members andr theiramelfrom. said; support; means carried .by the pendulousmembcr' and-acting .onxthe gyrozto cause. the spinexisi to. seek: thexvertical: :andcomprising an. .ele'ctro-. magnet carried by .therpendulousi..-member and acircular metallic. member .forming. a coaxial. part of-the. gyro motor-and provided with a sphericah surface rotatable .contiguously' to :the: electrons magnet to produce, dependent. upondeviationoi. the .rotor spin. axis from vertical and :due; toeddy current action; .a.,couple acting... on. the 'gyrocto; precess. the spin axisatmvertical, whereby deviar'. tion otthe spin axislfrom vertical-is opposed'and return of such axisitoverticalis effected; follow.- up means responsive tothe -.:gyro to; movethe. level member; relative-to the support to maintain.-

. its positionxirrespective of angular-.movementofi such. support; velectromagnetic 'meanszionapplying torque to the-frame about. an axistransverse tov the spin axis; said electromagnetic. :means comprising a cylindrical winding:componentrand; an armature component movable .thereaboutrinz spaced relation thereto; means for/mounting the cylindrical component on said. gyro pframe. axialialignmentwith the'rotor spin. axis; means. including a motor for mounting :thearmaturecomponent on the level memberand themotor. being. operative .to-.move the latter component about: the cylindrical component: to' locate. the magnetic ;torque. in a north-south. plane; and me ans providing: with the magneticmtorque e1?- fecti've in.:the north-south plane," for variation of the. excitation :of' theiwindin componentv to provide atorquewhichis adequatefor precession. of the gyro to compensate -for. the effect of earth's rotation to -maintain the rotor spin axis vertical.

9'." Imgyro'apparatus, a support movable angu-' larly with respect to the earth; a level member; aneutral gyro comprising a frame and a rotorjournaled'in the frame; apendulous bail; gimbal' means for supporting'th'e level member,- gyroand the bail'fromthe 'support; an-electromagnet 9 pendulously suspended by the bail so that normally its axis is in the vertical passing through the gyro center; a circular metallic member forming a coaxial part of the rotor and provided with a spherical surface rotatable contiguously to the electro-magnet to produce, dependent upon deviation of the spin axis from vertical and due to eddy current action, a couple acting on the gyro to precess the spin axis to vertical, whereby deviation of the spin axis from vertical is opposed and return of such axis to vertical is effected; means acting on the bail independently of the gyro to damp oscillatory movements of the bail and the electromagnet carried thereby; electromagnetic means for applying torque to the gyro in a northsouth plane to cause the latter to precess in the east-west plane; said electromagnetic means including a cylindrical winding component and an armature component movable about the latter in spaced relation thereto; means for mounting the cylindrical component on said gyro frame in axial alignment with the rotor spin axis; means including a motor for mounting the armature component on the level member and the motor being operative to locate said torque in a north-south plane; and means for varying the excitation of the winding of the winding component so that the gyro may be caused to precess in the east-west plane at the same rotational velocity as the earth and in the same direction as that of the earth.

10. In a gyro-vertical, the combination of, a neutral gyro comprising a casing and a rotor journaled therein; a pendulous member mounted so as to be capable of pendulous movement independently of the gyro; a damper for the pendulous member and operative independently of the gyro; erecting means includin the pendulous member, components carried by the pendulous member and by the gyro, respectively, and means providing for energization of the pendulousmember-carried component for action on the gyro-carried component so that the pendulous member may be effective to cause the rotor spin axis to precess to the vertical; and a frictional damper for damping nutational movements of the gyro; said frictional damper comprising an annular inertia member arranged coaxially of the gyro spin axis and means carried by the gyro casing and providing a normally horizontal bearing surface for the inertia member; said bearing surface and inertia member being relatively movable in response to nutational movement of the gyro to effect dissipation of nutational energy in friction between the inertia member and the bearing surface.

CLINTON R. HANNA. LAWRENCE B. LYNN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,141,099 Anschutz-Kaempfe June 1, 1915 1,183,745 Ledyard May 16, 1916 2,133,793 Anscott et a1 Oct. 18, 1938 2,133,809 Carter et a1 Oct. 18, 1938 2.158,048 Braddon May 9, 1939 I 2,190,698 Carter Feb. 20, 1940 2,293,092 Wittkuhns Aug. 18, 1942 2,328,744 Rotors Sept. 7, 1943 2,411,087 Ford et a]. Nov. 12, 1946 2,417,081 Lynn Mar. 11, 1947 

